12mm vs. 12mm - 50mm

As a 24mm equiv lover on my old DSLR gear, who really can't afford £500 odd for the super little 12mm prime for my EP-3 - I am wondering how the 12-50 would compare IQ wise, assuming working at apertures around f5.6/F8.0 - seeing they are beginning to appear on Ebay for around £250 - as unwanted with OM-D kits.